The present invention relates to a method and a system for preparing a liquid extract by passing water through a substance contained in a cell which is submitted to a centrifugation. More specifically, the invention is for preparing a beverage extract such as coffee and the like.
It is know to prepare beverages wherein a mixture consisting of brewed coffee and coffee powder is separated with centrifugal forces. Such a mixture is obtained by bringing liquid, such as hot water, and coffee powder together for a defined time. The liquid is then forced through a screen, on which screen powder material is present.
In certain methods such as in GB1506074, the cell comprises a large opening for enabling the coffee to be charged in the capsule. Then, liquid is filled in the cell and the cell is rotated. Normally, the cell is not entirely filled with liquid otherwise liquid would leak from the large opening due to the gradient of pressure which is created at the small discharge orifices.
EP079713 relates to a similar centrifugal apparatus with a cover that adjoins the filter element thus making a substantially closed filter cell. A problem is that if air cannot escape sufficiently rapidly through the filter and the restriction gap at the beginning of the brewing operation, air pockets can form in the cell. The air pocket can be prejudicial to the complete wetting and/or extraction of the substance and may create a rise of the pressure of liquid in the cell which volume is insufficient.
WO 2006/112691 relates to another centrifugal device comprising slits for feeding powder/water mixture and passes into the space delimited between a cylinder and a piston.
One problem of the centrifugal systems is that if too much gas remains in the cell, a limited volume of liquid can enter the cell. Therefore, there can be areas in the cell where the ingredients are not properly wetted. The quality of extraction is consequently affected negatively. In particular, if the powdered ingredients are not properly wetted, the discharged liquid experiences a poor extraction rate, i.e., a low total solid content (“Tc”).
Also, if an insufficient amount of liquid is introduced in the capsule, the centrifugal pressure for the liquid to leave the cell will become too elevated thereby requiring a too high rotational speed to make the liquid extract leaves the capsule.
Furthermore, the discharge openings made in the cell can be so small or, the discharge be even closed by a discharge valve, that the volume of gas cannot escape from these openings or valve correctly or timely. Accordingly, improvements in such devices are needed, and these are now provided by the present invention.